GLACIATION OF PRINCE WILLIAM SOUND 481
brief discussion of the similarities and contrasts of the two fields in which our own most detailed studies have been conducted,—Yakutat Bay and Prince William Sound.
Difference in Extent of Present Glaciers. We have no adequate records of precipitation for giving any basis whatsoever of a discussion of the comparative amount of snow that falls in these two areas, but there are some general considerations which lead us to-the belief that there is less supply for glaciers in the Prince William Sound region than in that of the coast further southeast. In the first place, although glaciers are numerous-and some of them large in the Prince William Sound region, they do not attain the magnitude of the glaciers along the straight coast which Yakutat Bay indents. Nor are there any of the piedmont glaciers and piedmont bulbs which characterize the central region from Controller Bay to Cross Sound and include such great ice bulbs as those of Bering, Malaspina, and La Perouse Glaciers. Another indication of the comparative weakness of the Prince William Sound type of glacier is the fact that there is not the same proportion of tidal glaciers as in Yakutat Bay. There are more tidal glaciers by actual count, but they are distributed over a far greater stretch of coast line. Furthermore, these tidal glaciers lie far back from the coast of the open ocean nearer the heart of the lofty mountains from which they are fed. The tidal glaciers are less active than those of Yakutat Bay. The great Columbia Glacier, for example, which is comparable to the Hubbard of Yakutat Bay, is far less active in iceberg discharge, and Columbia Bay is never so clogged with floating ice as to make navigation in small boats as difficult as in Yakutat Bay. Another point of contrast is the fact that neither the tidal glaciers nor those ending on the land in Prince William Sound appear to be parts of great through glacier systems comparable in size with those of the St. Elias and Fairweather regions. Although the valleys are ice-filled, and there are glacier passes, there does not seem ta be the same ice-drowned topography that characterizes the region further southeast.
These differences in the extent of present glaciation of the two regions is apparently due primarily to two significant facts. The first of these is the position and nature of the mountains. In the Yakutat Bay region the lofty mountains lie along the coast, whereas in the Prince William Sound region the coastal mountains are lower and the main range of lofty mountains lies farther inland. The Chugach Mountains are of sufficient height to give rise to many and large glaciers, but not to a glacier system such as the massive, broad, and elevated St. Elias-Fairweather Ranges nourish. The second reason for the difference is in exposure to moisture-laden winds. In both cases the prevailing winds from the ocean reach the glacier-feeding mountains^ but in the St. Elias-Fairweather mountains they reach the lofty chain without any intermediate barrier. To reach the mountains from which the Prince William Sound glaciers are fed, however, the west and southwest winds must first pass over a mountainous foreland on which a part of their vapor is necessarily condensed. Enough vapor still passes over this barrier and the glacier-supplying mountains are lofty enough to give rise to many large glaciers, but not to push them out to the mountain base, nor even to cause the tidal glaciers to discharge with the activity of those of Yakutat Bay.
Contrast in Size and Form of the Inlets. In a comparison of the glaciation of Yakutat Bay and Prince William Sound, and especially in considering the condition of former glaciation, it must be borne in mind that the two inlets are notably different in both size and form. As to size, Prince William Sound is several times as large as Yakutat Bay. In each case the form is divisible into two parts, a broad outer portion, and narrow inner